Large peripheral storage systems are advantageous for a substantial number of business and engineering software applications. In one configuration of such systems, storage is accomplished by distributing the data to be stored over a number of separate storage devices that cooperate together in defining a storage device array. Such individual storage devices may include, among other devices, magnetic and optical disk drives. Such storage systems have large storage capacities. Together with a host system, they contribute to high data transmission rates. Data reliability is also achieved using a storage device array.
The large capacity is achieved by using a number of relatively inexpensive storage devices, such as 5.25 inch magnetic disk drives. The high data transmission rates are achieved by configuring the system so that the individual storage devices are grouped into one or more "logical volumes or clusters." A logical volume, even though it is comprised of a number of physically separate storage devices, appears to the host system as a single, large storage unit. The storage array typically includes hardware and software to enable all storage devices in a logical volume to be simultaneously involved in data transmission. That is, each device has a unique data connection such that a read or write to the logical volume is accomplished by means of a read or write to each device in the logical volume. This allows large amounts of data to be rapidly read from or written to the storage array. High data reliability can be achieved by utilizing hardware components and software procedures for redundantly storing data, such as the use of parity information, together with one or more extra storage devices that can be used as replacements for storage device(s) that fail. Data on a failed device can be reconstructed, using the parity information, and transferred to the replacement storage device until the failed device is replaced.
A requirement associated with storage arrays is that the order or arrangement of the correct storage devices in each logical volume must be known and maintained. The storage array uses this order or sequence of storage devices in converting between the single stream of data interpretable by the host system and the multiple parallel data streams from/to a logical volume. This ordering of storage devices allows data being retrieved from the storage array, via parallel data transfers from storage devices in a logical volume, to be converted into a single stream of information acceptable to the host system.
Since replacement of individual storage devices might be necessary, there are a number of system maintenance situations that could arise and must be accounted for. For example, a storage device that is part of one logical volume could inadvertently be placed in another logical volume, thus making unreadable the data in the one logical volume. As another example, the storage devices within a logical volume could be incorrectly permuted such that the data supplied by the devices is not received through the proper data connection and thus cannot be properly converted. More specifically, it is known to store consecutively transmitted data bytes on separate disks. For example, for fixed sized data blocks, byte 1 is stored on disk one, byte 2 is stored on disk two, byte n is stored on disk n, byte n+1 is stored on disk one and so forth. To correctly reassemble the stored data from the multiple disks, it is critical that the same disks having the distributed data be accessed. If disk two, for example, has been replaced by another disk not having the stored data of disk two, a problem occurs because the data cannot be accurately reassembled using different data from such a disk. Similarly, if the physical locations or connections of disks one and two are switched, the data could not be accurately reassembled.
Such problems arise due to the lack of a mechanism for automatically determining if each storage device in the storage array is positioned in the correct location. It would therefore be advantageous to have a procedure by which a verification can be made that array storage devices are both logically clustered together and in the correct order within each logical volume.